This invention relates to improved apparatus and methods for conveying information from a downhole location deep within a well to the surface of the earth, in order to apprise a driller of one or more conditions which exist in the well.
During drilling of a well, it is essential in most instances that frequently updated information be obtained as to the conditions which exist at the bottom of the well. For example, the inclination of the lower portion of the drill string and the direction of that inclination are often of critical importance, particularly in directional drilling, in order to assure that the hole is drilled along an intended path. Similarly, it may be desirable to convey to the surface of the earth information relative to temperature and pressure conditions at the bottom of the hole, the weight which is applied to the bit at a particular instant, and other parameters important to ulimate completion of a satisfactory drilling operation.
In the past, much of this downhole information has been obtained by instruments which have been lowered into the drill string on a wire line, and which after obtaining the information are withdrawn upwardly from the drill string before the drilling operation can be continued. In order to avoid the necessity for lowering an instrument into the drill string on a wire line, attemps have been made to devise systems for conveying information from a downhole location to the surface of the earth by telemetry not requiring a wire line. Some of these systems contemplate development of pressure pulses in the drilling fluid, with sensors being employed at the surface of the earth for responding to those pressure pulses and producing an output therefrom representing the downhole information. In some instances, a pressure pulse is produced by momentarily bypassing some of the circulating fluid at a location above the bit from the interior of the drill string to its exterior. In other types of equipment, a pressure pulse has been caused by closing a valve through which drilling fluid flows downwardly within the drill string and toward the bit. In either case, the surface equipment responds to the momentary increase or decrease in pressure resulting from actuation of a valve at the downhole location.